Computers, servers, communication devices, workstations, and the like store data in memory modules that typically receive pre-regulated electrical power from the motherboard through a single module interface connector. Multiple regulated bias voltages are usually supplied and can include, for example, a dynamic random access memory (DRAM) memory integrated circuit (IC) positive power supply voltage (VDD), a DRAM input/output (I/O) driver positive power supply voltage (VDDQ), and a DRAM I/O reference supply voltage (VREF). VREF is usually low current and supplied over a single input pin. VDD and VDDQ and respective return lines (VSS and VSSQ) are applied through multiple pins that are distributed along the module interface connector.
Memory module power systems have difficulty maintaining constant reference voltages for several reasons. For example, the remote location of regulator output from memory device integrated circuits on memory modules limits regulator transient load response time. The large output capacitance that is used to address the wide range of the regulator output current supply additionally limits transient response time. Furthermore, system board switching regulation produces high frequency switching noise that is imposed on memory module bias voltages, alters memory module timing, and limits actual memory operating speed.
To attain higher speed memory module performance, even for large memories, significant limiting factors, including factors associated with memory system power generation, regulation, and distribution are to be addressed.
As memory technology advances and voltages are reduced to improve power consumption, tolerances for voltage also decrease. Maintaining specified voltage levels on memory modules (such as dual in-line memory modules (DIMMs)) across memory subsystems becomes much more difficult. Maintaining the specified voltage levels is particularly difficult across multiple memory configurations with different power specifications, therefore causing power drops across the power plane.